Apparatus for continuous reforming-regeneration process

ABSTRACT

AN APPARATUS SYSTEM FOR OPERATING A CONTINUOUS REFORMING-REGENERATION PROCESS COMPRISING A PLURALITY OF STACKED REFORMING REACTORS AND EMPLOYING A PLATINUM CATALYST WHEREIN CATALYST ACTIVITY IS MAINTAINED AT A PREDETERMINED LEVEL BY CONTINUOUS REGENERATION THEREOF WITHOUT THE REMOVAL OF ANY REACTOR FROM THE PROCESS STREAM.

p 1972 A. R. GREENWOOD ET AL 3,692,496

APPARATUS FOR CONTINUOUS REFORMING-REGENERATION PROCESS Filed April 19, 1971 MW NW //V VE/V TOPS: Arthur R. Greenwood Kenneth D. Vase/y A TTORNEYS United States Patent Int. Cl. 301i 9/12 11.5. C]. 23288 G 6 Claims ABSTRACT OF THE DISCLOSURE An apparatus system for operating a continuous reforming-regeneration process comprising a plurality of stacked reforming reactors and employing a platinum catalyst wherein catalyst activity is maintained at a predetermined level by continuous regeneration thereof without the removal of any reactor from the process stream.

This application is a division of our copending application Ser. *No. 860,905, filed Sept. 25, 1969 and now US. Pat. No. 3,647,680 issued Mar. 7, 1972.

The reforming of hydrocarbon feed stocks, such as a naphtha fraction derived from petroleum, utilizing a platinum group metal-alumina catalyst, is a process Well known in the art. Briefly, a naphtha feed stock is admixed with hydrogen and contacted with the catalyst, usually in a fixed bed reaction zone, at reforming conditions of temperature and pressure to cause at least a portion of a naphtha feed stock to be upgraded to products of improved octane value. Prior art reforming proceses generally comprise one of two types of operation, i.e., a nonregenerative type and a regenerative type. In the practice of a non-regenerative type of operation, the catalyst is maintained in continuous use over an extended period of time, say from about 5 months to about a year or more depending on the quality of the catalyst and the nature of the feed stock. Following this extended period of operation, the reforming reactor is taken off stream while the catalyst is regenerated or replaced with fresh catalyst. In the practice of the regenerative type of operation, the catalyst is regenerated with greater frequency utilizing a multiple fixed bed reactor system arranged for serial fiOlW of the feedstock in such a manner that at least one reactor can be taken off stream while the catalyst is regenerated or replaced with fresh catalyst, one or more companion reactors remaining on stream, or going on stream, to replace the off stream reactor. Subsequently, the regenerated fixed bed reactor is placed on stream while another is taken off stream and the catalyst bed is regenerated or replaced With fresh catalyst in like manner.

It is apparent from the brief description of prior art non-regenerative and regenerative reforming processes that both means of operation embody certain undesirable features. For example, in the non-regenerative type of operation, the entire plant is usually taken off stream to effect regeneration or replacement of the catalyst with a resultant significant loss in production. Further, the nonregenerative type of operation is characterized by a continuing decline in catalyst activity during the processing period requiring an operation of increasing severity to maintain product quality, usually at the expense of product quantity. In the regenerative type of operation utilizing a multiple fixed bed reactor system, or swing reactor" system, similar problems are encountered although to a lesser degree. However, the start up and shut down procedures relating to insertion and removal of a reactor in ice the process stream are unduly complicated and require a complex system of valves, lines and other equipment to accomplish reactor changeover with a minimum loss of process time.

It is therefore desirable to provide a reforming process which would substantially obviate the undesirable features of prior art non-regenerative and regenerative type reforming processes. More specifically, it would be desirable to have a reforming process whereby a predetermined high level of catalyst activity and stability is maintained without resorting to the removal of the reforming reactor from the process stream and a consequent loss of process time.

Accordingly, it is an object of this invention to present an improved catalytic reforming process whereby a predetermined high level of catalyst activity and stability is maintained over extended periods of time. Thus, in accordance with one embodiment of this invention, there is provided a method of operating a continuous reformingregeneration process employing a platinum group metal catalyst which comprises pre-heating a hydrogen-hydrocarbon reaction mixture to reforming temperature, charging the reaction mixture to a reactor and treating the reactant stream therein at reforming conditions in contact with a moving bed of catalyst particles; withdrawing used catalyst particles from the said reactor while maintaining the same on stream at reforming conditions; passing the catalyst particles to a regenerator comprising in sequence a carbon burn-off zone, a halogenation zone and a drying zone; moving said particles through said carbon burn-off zone, charging an oxygen-containing gas thereto in contact with said particles and recycling at least a portion of the resulting flue gases to said carbon burn-off zone to effect a controlled burning and removal of carbon from said particles; passing the particles substantially free of carbon in a continuing moving bed through said halogenation zone in contact with steam admixed with halogen in a mole ratio of at least about 1:1 and diluted with air to effect halogen addition thereto; passing the halogenated particles in a continuing moving bed through said drying zone and drying said particles therein in contact with a stream of hot, dry air; Iwithdrawing catalyst particles from said drying zone, treating the same in contact with hydrogen at a temperature of from about 800 to about 1200 F., and adding the reduced catalyst particles to the catalyst contained in the aforesaid reactor to elfect a substantially constant catalyst inventory therein.

Another embodiment includes the above method wherein the catalyst particles from said drying zone and hydrogen are processed downwardly as a moving bed through a confined reduction zone in the upper portion of the reforming reactor to effect an indirect heat exchange relationship with the hot reaction mixture charged thereto whereby said catalyst particles are reduced in contact with hydrogen at a temperature of from about 800 to about 1200 F., the reduced catalyst particles being processed downwardly and added to the moving catalyst bed contained in said reactor to elfect a substantially constant inventory therein.

Other objects and embodiments of this invention will become apparent in the following detailed specification.

The catalyst employed in the practice of this invention comprises a platinum group metal, combined halogen and alumina, the platinum group metal and combined halogen preferably being composited with a spherical alumina such as prepared by the oil drop method described in US. Patent No. 2,620,314 issued to James Hoekstra. Preferably, the catalyst will comprise platinum and combined chlorine composited with alumina. It is understood that the catalyst may further include a promoter, such as rhenium, as practiced in the art. Other platinum group metals including palladium, rhodium, ruthenium, osmium and iridium are suitable although less commonly employed. Also, other refractory inorganic oxides including silica, zirconia, boria, thoria, etc, as well as composites thereof such as silica-alumina, alumina-boria, and the like, may be used with satisfactory results. Generally, the platinum group metal will comprise from about 0.01 to about 5.0 wt. percent of the catalyst composite, from about 0.10 to about 0.80 wt. percent being preferred. While the halogen component may be chlorine, bromine, fluorine and/ or iodine, chlorine is most usually utilized to impart the desired acid-acting character to the catalyst. The halogen component suitable comprising from about 0.50 to about 1.5 wt. percent of the catalyst composite, is measured as elemental halogen although present in a combined form with one or more of the other catalyst components. Those skilled in the art are familiar with the preparation of the reforming catalyst herein contemplated and, since the novelty of the present invention does not reside in the catalyst per se, a further detailed description is not warranted.

Catalytic reforming conditions include a temperature of from about 700 to about 1000 F., a pressure of from about 50 to about 1000 p.s.i.g., a liquid hourly space velocity of from about 0.2 to about 10, and a hydrogen to hydrocarbon mole ratio of from about 1:1 to about 1. The method of this invention is particularly adapted to low pressure reforming, preferably at a pressure of from about 50 to about 200 p.s.i.g. Since the reforming reaction is endothermic in nature, in the event a multiple reactor system is employed, the effluent from a given reactor is generally reheated to reaction temperature prior to introduction into the next succeeding reactor.

As used herein, the term activity relates to the capacity of the catalyst system to convert the low octane naphthe. feed stock to a relatively high octane product, for example, a gasoline fraction with an octane rating in excess of about 90, at a given temperature, pressure and space velocity. The concept of the present invention permits reforming of the hydrocarbon feed stock in contact with a catalyst system characterized by a substantially constant activity level. This is accomplished in part by the method of this invention which provides for the constant replacement of used catalyst in the system with regenerated catalyst whereby the catalyst system remains at a substantially constant activity level at a given temperature, pressure and space velocity. This is in contrast to conventional non-regenerative and regenerative operations where catalyst activity is maintained at a constant level by increasing the severity of the operation.

In the schematic drawing, the reactant stream is depicted as being processed through a multiple reactor system comprising two vertically stacked reactors with intermediate heating of the reactant stream between reactors. However, it is understood that the reactant stream may be processed through a multiple reactor system comprising reactors arranged side-by-side in the common fashion and with intermediate heating of the reactant stream between reactors to maintain desired reforming temperatures in the various reactors. It is further understood that a single reactor system may be employed, or any combination of the described systems. In the multiple reactor system, fresh or reconditioned catalyst may be continuously added to an initial or top reactor and processed serially or sequentially through the reactor system, the catalyst being withdrawn from the final or bottom reactor, as the case may be, for reconditioning in accordance with the method of this invention. Alternatively, fresh or reconditioned catalyst may be continuously added to each of two or more reactors, the catalyst being withdrawn from each of said reactors in incremental amounts for reconditioning according to the method of this invention. In the latter case, the used catalyst from the various reactors is commingled in a common hopper, regenerated according to the method of this invention, and subsequently distributed to said re- 4 actors as required to maintain a substantially constant catalyst inventory therein. Alternatively, the catalyst of a selected reactor may be periodically regenerated while maintaining all reactors of the system, including the selected reactor, on stream at reforming conditions.

In the preferred multiple reactor system comprising stacked reactors, the reactor system will in effect have a common catalyst bed moving as a substantially unbroken column of particles from the top reactor to the bottom reactor. Thus, used catalyst is withdrawn from the bottom reactor while regenerated catalyst is added to the top reactor, and the catalyst of the reactor system is regenerated with all reactors remaining on stream at reforming conditions.

Referring then to the drawing, and at the same time setting forth an illustrative operation, a straightrun gasoline fraction boiling in the ZOO-400 F. range is charged to the process through line 1 at a liquid hourly space velocity of about 2.0, entering a heater 2 in admixture with a hydrogen-rich gas stream recycled through line 3 from a product separator not shown. In a conventional reforming operation, a considerable excess of hydrogen is admixed with the hydrocarbon charge to minimize carbon formation on the catalyst. Typically, hydrogen is employed in about a 10:1 mole ratio with the hydrocarbon charge. However, the method of this invention, wherein the catalyst is subjected to frequent regeneration, affords a substantial reduction in hydrogen consumption. Preferably, the hydrogen-hydrocarbon mole ratio is from about 1:1 to about 5:1. Thus, in the present illustration, the heated combined stream comprises hydrogen and hydrocarbon in a mole ratio of about 3:1, said heated combined stream being withdrawn from the heater 2 by way of line 4 and charged into the upper portion of reforming reactor 5.

Reforming reactor 5 is shown in vertical alignment with reforming reactor 11, with an intermediate heater 10. The reforming catalyst charged to reactor 5, as hereinafter described, is comprised of spherical diameter particles containing about 0.375 wt. percent platinum and 0.9 wt. percent combined chlorine, the remainder being alumina. The reactor temperatures are maintained in the 850-950 F. range and the pressure at about 200 p.s.i.g. Reforming reactor 5 is shown with catalyst confined in an annular moving bed 6 formed by spaced cylindrical screens 7. The reactant stream is passed in an out-to-in radial flow through the catalyst bed, the reactant stream continuing downwardly through the cylindrical space 8 formed by said annular bed 6 and exiting to heater 10 by way of line 9. Since the reaction is endothermic, the effiuent from the reactor 5 is re-heated in heater 10 and thereafter charged to reactor 11 through line 12. Again, the reactants stream is passed in an out-to-in radial flow through the annular catalyst bed 13 substantially as described with respect to reactor 5, the flow passing downwardly through the cylindrical space 14 and passing from reactor 11 by way of line 15. The reactor effluent withdrawn through line 15 is passed to conventional product separation facilities for recovery of high octane product, for example, a reformate having a clear octane number rating of about 95, and recovery and recycle of a hydrogen-rich gas stream to the reactor system.

The catalyst particles descending through the reactor 5 as an annular moving bed 6, are continued to the annular moving bed 13 of reactor 11 by way of catalyst transfer conduits 16 and 17. Conduits 16 and 17 represent a multitude of catalyst transfer conduits permitting passage of the catalyst between said annular beds 6 and 13 and effecting a suitable pressure drop whereby substantially all of the reactant stream from reactor 5 is directed through the heater 10 by way of line 9 with only a minimal amount by-passing said heater 1'0 and passing directly to reactor 11 together with the catalyst flow through conduits 16 and 17. Thus, in effect, the reactor system has a common catalyst bed moving as a substantially unbroken column of particles through the top reactor and the bottom reactor 11. In the present example, the used catalyst is withdrawn through lines 18 and 1-9 at a rate such that the catalyst inventory of the reactor system is replaced in 30 day cycles. The catalyst is withdrawn intermittently through line 20 and by means of control valve 21 to effect a moving bed type of operation, the catalyst being discharged into a lock-hopper 22 for separation of residual hydrocarbon therefrom. The used catalyst is subsequently transferred through line 23 and control valve 24 to a lift engager 25 to be lifted in a nitrogen stream to a disengaging hopper 28 by way of line 27. The catalyst is lifted to said hopper 28 by a fiow of nitrogen charged to the lift engager 25 through line 26 from an external source not shown. Nitrogen is charged to the lift engager 25 at the rate of about 531 standard cubic feet per hour and at a temperature of about 100 F.

The used catalyst deposited in the disengaging hopper 28 comprises about 0.7 wt. percent combined chloride and 2-5 wt. percent carbon. An overhead line 29 is provided to vent the disengaging hopper 28 to the atmosphere or to recycle the nitrogen. Catalyst particles from the disengaging hopper 28 are fed through line 30 to a catalyst regenerator comprising a carbon burn-off zone 31, a chlo rination zone 32, and a drying zone 33. The catalyst particles are processed downwardly as a moving bed or column in a confined regeneration zone 34, passing from the carbon burn-off zone 31 to the chlorination zone 32. Chlorinated and substantially carbon-free particles are then continued downwardly through the drying zone 33 and contacted therein with a hot, dry air fiow to effect the separation of excess adsorbed gaseous components from the catalyst.

In the present example, the catalyst particles are passed from the disengaging hopper 28 to the catalyst regenerator at an average rate of about 200 pounds per hour. The catalyst particles are processed downwardly through the carbon burn-oft zone 31 at a rate to establish an average residence time therein of about 2 hours.

In the carbon burn-off zone 31, the catalyst particles are heated in contact with an oxygen-containing gas including hot recycle gases charged to the carbon burn-ofi zone 31 at a gaseous hourly space velocity of about 4700 by way of line 44. The oxygen-containing gas is derived from air charged to the drying zone 33 by way of line 35, the air becoming admixed with steam, chlorine, and HCl on passing upwardly through the chlorination zone 32, and the gaseous mixture continuing upwardly through the carbon burn-off zone 31 in contact with the catalyst particles contained therein. The resulting gaseous products, including oxides of carbon and sulfur, are withdrawn from the carbon burn-ofi zone 31 as flue gases through line 36. In some cases, it may be desirable to separate sulfur components from the flue gases prior to recycle. In that event, the flue gases are charged to a scrubber 37 wherein they are admixed with a caustic stream recycled from a caustic settling tank 40 through a cooler 65 and line 38. The mixture is then passed to the caustic settling tank via line 39. The resulting flue gases, substantially free of halogen and oxides of sulfur, are recovered overhead from the settling tank 40 through line 41 and charged by means of a blower 42 through a heater 43 and line 44 to the carbon burn-off zone 31 as aforesaid. The heater 43 is provided for start-up operation. The gases recycled to the carbon burn-off zone 31 comprise about 0.7 wt. percent oxygen to effect a controlled burning at a temperature of from about 830 to about 930 F. in the burnoff zone. An overhead vent line 45 is provided to discharge excess flue gas from the process.

The catalyst particles, substantially free of carbon are processed downwardly from the carbon burn-off zone 31 through the chlorination zone 32 at conditions to efiect an average residence time therein of about 1 hour. In the chlorination zone 32, the catalyst particles are brought in contact with about a 2:1 mole ratio of steam and chlorine charged thereto through line 46, the steam and chlorine being admixed with air passing upwardly from the drying zone 33 as previously mentioned. Steam is charged to the system at a temperature of about 450 F. and at a rate of about 2.4 pounds per hour through line 47. The steam is passed through line together with recycle vapors contained therein and admixed with chlorine from line 48, the chlorine being charged at a rate of about 1.45 pounds per hour. The steam-chlorine mixture is heated to about 930 F. in heater 49 and charged to the chlorination zone 32 through line 46 at a gaseous hourly space velocity of about 4700. A recycle stream comprising excess steam and chlorine is withdrawn from the chlorination zone 32 by way of line 50 and circulated by means of a blower 51 as a portion of the steam-chlorine charged to the chlorination zone 32.

From the chlorination zone 32, the catalyst particles are continued downwardly through the drying zone 33 whereby vaporous components are stripped from the catalyst by a flow of dry air. The air is charged to the system through line 52 from an external source not shown and heated to 800-l000 F. in heater 53 prior to being charged to the drying zone 33 through line 35. The air is charged at a gaseous hourly space velocity of about 150.

The catalyst particles are withdrawn from the regenerator at regular intervals by way of line 54 through control valve 55 and collected in lock-hopper 56. The catalyst is subsequently transferred to a lift engager 57 through line 58 and control valve 64 to be conveyed to the reforming reactor 5. The catalyst particles are carried through line 60 by a dry, pure hydrogen stream introduced to the lift engager 57 by way of line 59 at about 3300 standard cubic feet per hour and at a temperature of about ambient. The hydrogen is subsequently used as a reducing gas and as a portion of the hydrogen feed to the reforming reactor 5.

Prior to direct contact with the reactant stream in reforming reactor 5, the catalyst, in admixture with hydrogen, is processed in a dense phase through a reducing zone 61 to effect an indirect heat exchange with hot reaction gases charged to said reactor. The catalyst is processed downwardly through the reduction zone 61 at a rate to establish a residence time of about 2 hours therein at a temperature of 9501000 The resulting reduced catalyst is thereafter added to the catalyst bed through lines 62 and 63 replacing that withdrawn from the reactor system through lines 18 and 19 for regeneration.

The method of this invention finds particular application with respect to low pressure reforming. While 10w hydrogen partial pressures favor the main octane-improving reactions, e.g., dehydrogenation of parafiins and naphthenes, a principal objection to low pressure reforming is in the excessive formation of carbon resulting from condensation and polymerization reaction also favored by low hydrogen partial pressures. However, the continous reforming-regeneration process of this invention substantially obviates this objection, and the relative catalyst instability resulting from carbon formation is no longer a limiting factor to a successful low pressure reforming operation.

An added advantage derived from the practice of this invention is in the increased and continued supply of hydrogen available for hydrogen-consuming refinery operations, such as hydrocracking.

We claim as our invention:

1. A multiple-stage reactor system for reforming a hydrocarbon stream in the presence of catalyst particles that are movable by gravity flow, which comprises in combination:

(a) a. vertically elongated confined chamber;

(b) at least two vertically-spaced reactor sections disposed within said chamber, with such sections having an inner cylindrical screen and an outer cylindrical screen spaced concentrically from the inner screen and from the wall of said chamber to define an annular catalyst bed section;

(c) said screen additionally defining in each section an inner manifold within the interior space of said inner cylindrical screen and an outer annularly-shaped manifold space between said outer cylindrical screen and said chamber;

(d) a transverse partition below each catalyst section and separating vertically adjacent reactor sections;

(e) inlet means connective to the outer manifold of each reactor section for introducing the hydrocarbon reactant stream thereto;

(f) outlet means connective with the inner manifold of each section for removing a fluid stream therefrom;

(g) conduit means serially connecting the outlet means associated with a superposed reactor to heat-exchange means and to the inlet means and the outer manifold space of the next successive lower reactor section for radial flow contact with the annular catalyst bed in such section;

(h) catalyst inlet means connective with the uppermost catalyst bed section for introducing catalyst thereto;

(i) catalyst outlet means connective with the lowermost catalyst section for withdrawing contacted catalyst therefrom and from said chamber; and,

(j) catalyst transfer conduit means connective between said spaced apart catalyst bed sections for removing catalyst by gravity flow from an uppermost section to a lowermost section.

2. The reactor system of claim 1 further characterized in that said catalyst transfer conduit means comprises a multiplicity of elongated uniformly spaced, relatively small conduits to provide a pressure drop substantially precluding reactant stream flow therethrough.

3. The reactor system of claim 1 further characterized in that said catalyst inlet means includes an elongated tubular section above the uppermost annular-form catalyst bed section, and distribution means is provided at the lower end of said tubular section to divide and pass the catalyst flow therethrough into each of a plurality of tubular means connecting to the uppermost catalyst sec tion, and the reactant stream inlet means to the uppermost reactor section is connected with the interior of an extended housing section at the top of said chamber which encompasses said elongated tubular section for said catalyst inlet, whereby there is heat exchange of the reactant stream flowing into said chamber around said tubular section prior to the reactant stream flow passing around the uppermost annular catalyst section.

4. The multiple-stage reactor system of claim 1 further characterized in that multiple-stage regeneration apparatus for regenerating used catalyst is interconnected therewith by catalyst withdrawal and lift means from said catalyst outlet means carrying to the top of a second vertically elongated confined chamber as a part of said regeneration apparatus and a catalyst withdrawal and lift means connects from the lower end of the latter to said catalyst inlet means for said uppermost catalyst reactor section, said second vertically elongated chamber having in combination therewith:

(a) spaced apart vertical screen means defining an elongated catalyst section therethrough and inlet and outlet manifold sections thereto on opposing sides thereof;

(b) transverse partitioning means in said chamber defining at least an upper carbon burn-off section and a next lower chlorination section;

(c) air inlet means connective to an inlet manifold for said carbon burn-0E section;

((1) outlet means connective with an outlet manifold for said carbon burn-01f section for discharging unreacted oxygen containing gas and combustion products therefrom;

(e) inlet means connective with an inlet manifold adjacent said chlorination section for introducing a chlorine containing gas transversely therethrough; and,

(f) outlet means connective to an outlet manifold for said chlorination section.

5. The multiple-stage reactor-regenerator apparatus system of claim 4 still further characterized in that said catalyst bed section in said second elongated chamber extends downwardly from said chlorination section into a further depending catalyst drying section, whereby catalyst withdrawal from said chamber is made from the lower end of the latter section, and a heated air inlet means is provided to the lower portion of said drying section and to said catalyst bed section, whereby the air can rise upwardly therethrough to commingle with the chlorine containing gas stream being passed transversely through the next superposed section.

6. The multiple-stage reactor-generator apparatus system of claim 4 still further characterized in that said gas outlet means from said carbon burn-off section connects with a flue gas recycle system including:

(a) a gas scrubber with means to contact said flue gas stream with a caustic stream; (b) a caustic removal and recovery tank; (0) recycle means between the latter and said scrubber; (d) washed gas transfer means to a heater means; and, (e) gas conduit means from the latter to said carbon burn-off section inlet means.

References Cited UNITED STATES PATENTS 1,982,099 11/ 1934 Heckenbleikner 23-288 G X 1,995,293 3/1935 Clark 23-288 G X 2,317,379 4/1943 Hemminger 23-288 G X 2,626,857 1/1953 Crowley 23-288 G 2,726,146 12/1953 Shirk 23-288 G 2,734,805 2/1956 Savage et a1. 23-288 G 2,745,724 5/1956 Kollgaard 23-288 G 2,758,059 8/1956 Berg 208-169 X 2,776,876 1/1957 Bowles 23-288 G 2,809,922 10/1957 Berg et al. 23-288 G X 2,893,942 7/1959 Berg 23-288 G X BARRY S. RICHMAN, Primary Examiner US. Cl. X.R.

23-288 B, 288 C, 288 H; 208-65, 140, 169, 252-415, 418 

